It is known that to transmit large quantities of information by means of radio signals, it is preferable to use broad-band polarized signals with high carrier frequencies.
In addition, when the same antenna serves both to transmit and to receive signals, it is necessary for the transmission frequency bands to be distinct from the reception frequency bands.
The ever increasing quantity of telecommunications traffic means that the transmission and reception frequency bands are being enlarged. For example, C band, used at present for certain satellite communications, and extending from 3.625 GHz to 4.2 GHz for reception and from 5.85 GHz to 6.425 GHz for transmission, is going to be expanded at its lower frequent limit for reception (3.4 GHz to 4.2 GHz) and at its upper frequency limit (5.85 GHz to 6.65 GHz) for transmission.
FIG. 1 is a diagram showing an antenna source that can be used for transmitting and receiving signals in conventional C band, i.e. with bandwidths of 575 MHz both for transmission and for reception. That known antenna source includes a radiating element such as a horn 10 connected via a matching section 12 and via a circular-section waveguide 14 to a polarizer 16 serving firstly to convert the received signals from circularly polarized signals into linearly polarized signals, and secondly to convert the signals to be transmitted from linearly polarized signals to circularly polarized signals.
The polarizer 16 is connected to a transducer 18 for separating the transmission frequencies from the reception frequencies. The transducer comprises a circular-section waveguide whose outside surface is provided with slots extending in the longitudinal direction--i.e. their long dimensions are parallel to the axis of the waveguide--and connected to other waveguides (not shown) and to filter means (not shown either) for blocking the transmission frequencies and passing the reception frequencies.
The end of the waveguide of the transducer 18 that is remote from its end connected to the polarizer 16 receives the signals to be transmitted. The transmission path includes filter means for blocking the reception frequencies and, in general, it also includes orthogonal polarization means.
It has been observed that an antenna source of that type does not give satisfactory results for transmitting and receiving broad-band signals, in particular for the above-mentioned expanded C band.